Semiconductor device having a multilayer interconnection structure

ABSTRACT

A semiconductor device includes a multilayer interconnection structure including an organic interlayer insulation film in which a conductor pattern is formed by a damascene process, wherein the organic interlayer insulation film carries thereon an organic spin-on-glass film.

This application is a continuation of prior application Ser. No.09/274,976 filed Mar. 23, 1999 now U.S. Pat. No. 6,417,116 which ishereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention generally relates to semiconductor devices andmore particularly to a semiconductor device having a multilayerinterconnection structure and a fabrication process thereof.

It is well known that the operational speed of a semiconductor deviceincreases according to the scaling law with miniaturization of thesemiconductor device. Thus, intensive efforts are being made in the artof semiconductor technology to miniaturize semiconductor devices as muchas possible.

Meanwhile, recent highly miniaturized, high-speed semiconductorintegrated circuits generally use a multilayer interconnection structurefor interconnecting individual semiconductor devices included in theintegrated circuit. In such high-speed semiconductor integratedcircuits, there occurs a problem of delay in the signals that aretransmitted through the interconnection pattern of the multilayerinterconnection structure as a result of the existence of straycapacitance.

Thus, in order to eliminate the problem of signal delay in themultilayer interconnection structure, there is a proposal to replace anSiO₂ film conventionally used in a multilayer interconnection structureas an interlayer insulation film, by an organic insulation film such asa hydrocarbon film. Further, there is a proposal to replace the Alpattern conventionally used for the interconnection pattern inmultilayer interconnection structure by a Cu pattern. By using anorganic insulation film having a dielectric constant of typically about2.5, it is possible to reduce the dielectric constant of the interlayerinsulation film as much as 40% as compared with the case of using aconventional SiO₂ interlayer insulation film.

When Cu is used for the interconnection pattern in a multilayerinterconnection structure, it is necessary to form the interconnectionpattern by a damascene process in view of the difficulty of applying adry etching process to such a Cu pattern.

FIGS. 1A and 1B show the fabrication process of a conventionalsemiconductor device that uses an organic insulation film for aninterlayer insulation film.

Referring to FIG. 1A, a substrate 11, on which various diffusion regions(not shown) are formed, is covered by a hydrocarbon insulation film,such as the SiLK (trade name of Dow Chemical, Inc.) by a spin-coatingprocess, wherein the hydrocarbon insulation film thus formed ispatterned to form an interlayer insulation film 12 in which a number ofgrooves are formed for accommodating interconnection patterns. Theinterlayer insulation film 12 is then covered by a TiN film 13 depositedby a sputtering process generally with a uniform thickness, and a Culayer 14 is deposited further on the TiN film 13 by a sputtering processso as to fill the foregoing grooves.

Next, in the step of FIG. 1B, the Cu layer 14 is subjected to a chemicalmechanical polishing (CMP) process and the part of the Cu layer 14locating above the interlayer insulation film 12 is removed. Thereby astructure in which a Cu pattern 14A fills the groove in the interlayerinsulation film 12 is obtained as indicated in FIG. 1B.

On the other hand, such a conventional fabrication process of asemiconductor device that includes the CMP process has a problem, asrepresented in FIG. 1B, in that the organic interlayer insulation film12 may also be polished together with the Cu layer 14 as a result of theCMP process. When this occurs, the Cu pattern 14A cannot be formed inconformity with the desired design specification.

In order to overcome the foregoing problem, it has also been practicedto form an SiO₂ film 12A on the surface of the organic interlayerinsulation film 12 by a CVD process as indicated in FIG. 1C. In thiscase, the CMP process is conducted while using the SiO₂ film 12A as apolishing stopper. In the case of polishing the Cu layer 14 by a slurryof Al₂O₃, the SiO₂ film 12A thus formed is substantially immune to thepolishing process, and the Cu pattern 14A and the interlayer insulationfilm are formed to have a desired thickness.

On the other hand, the structure of FIG. 1C has a drawback in that theSiO₂ film 12A on the organic interlayer insulation film 12 has a verylarge dielectric constant of about 4.0. In such a case, there tends tooccur a concentration of electric flux in the SiO₂ film 12A and thestray capacitance of the interconnection pattern 14A tends to increaseeven when the low-dielectric organic interlayer insulation film 12 isused for the multilayer interconnection structure.

Further, the conventional structure of FIG. 1C has a drawback in thatthere may occur a short-circuit in the interconnection patterns that areformed in the upper layers locating above the interlayer insulation film12 when the interconnection pattern 14A in the interlayer insulationfilm 12 is formed to have a large width.

FIGS. 2A–2D show the process of forming two interconnection layers basedon the structure of FIG. 1C, wherein those parts corresponding to theparts described previously are designated by the same reference numeralsand the description thereof will be omitted.

Referring to FIG. 2A, the Cu layer 14 is formed in the interlayerinsulation film 12 so as to fill a groove 12G in the interlayerinsulation film 12, and a CMP process is conducted in the step of FIG.2B in correspondence to the step of FIG. 1B to form the Cu pattern 14Afilling the groove 12G.

As indicated in FIG. 2B, such a CMP process inevitably causes a dishingin the interconnection pattern 14A when the width of the groove 12G islarge. Thus, when a next interlayer insulation film 15 is formed on theinterlayer insulation film 12 thus including the interconnection pattern14A, there appears a depression 15A on the surface of the interlayerinsulation film 15 in correspondence to the dishing of theinterconnection pattern 14A as represented in FIG. 2C.

Thus, when a further organic interlayer insulation film 16 is formed onthe interlayer insulation film 15 with grooves 16A and 16B formedtherein in correspondence to the interconnection pattern 14A asrepresented in FIG. 2D, Cu patterns 18A and 18B, formed by a depositionof a Cu layer on the interlayer insulation film 16 and a subsequent CMPprocess so as to fill the grooves 16A and 16B, may be connected witheach other by a bridging part 18C of Cu. It should be noted that such abridging part 18C remains after the CMP process due to the depression15A of the underlying interlayer insulation film 15 and hence thedishing of the wide interconnection pattern 14A. In such a structure,there occurs a short-circuit between the interconnection pattern 18A andthe interconnection pattern 18B.

SUMMARY OF THE INVENTION

Accordingly, it is a general object of the present invention to providea novel and useful semiconductor device and a fabrication processthereof wherein the foregoing problems are eliminated.

Another and more specific object of the present invention is to providea semiconductor device having a multilayer interconnection structureincluding therein an organic interlayer insulation film and a conductorpattern formed in the organic interlayer insulation film by a damasceneprocess, wherein a polishing stopper layer resistant to a CMP processand having a low dielectric constant is provided on a surface of theorganic interlayer insulation film.

Another object of the present invention is to provide a semiconductordevice having a multilayer interconnection structure including anorganic interlayer insulation film and a conductor pattern formedtherein by a damascene process, wherein the problem of short-circuit ofthe interconnection patterns formed above the foregoing conductorpattern, caused by a dishing of the conductor pattern, is eliminated.

Another object of the present invention is to provide a method offabricating a semiconductor device, comprising the steps of:

forming an interlayer insulation film on a substrate;

forming an organic spin-on-glass film on said interlayer insulationfilm;

patterning said organic spin-on-glass film and said interlayerinsulation film to form a depression such that said depressionpenetrates through said organic spin-on-glass film and reaches saidinterlayer insulation film;

depositing a conductor layer on said organic spin-on-glass film so as tofill said depression; and

removing a part of said conductor layer locating above said organicspin-on-glass film by a chemical mechanical polishing process, to form aconductor pattern filling said depression, said chemical mechanicalpolishing process being conducted while using said organic spin-on-glassfilm as a polishing stopper.

Another object of the present invention is to provide a semiconductordevice, comprising:

a substrate;

an interlayer insulation film formed on said substrate;

another insulation film formed on said interlayer insulation film;

a depression penetrating through said another insulation film andreaching said interlayer insulation film; and

a conductor pattern filling said depression;

said another insulation film being formed of an organic spin-on-glass.

According to the present invention, it is possible to form theinterlayer insulation film and the conductor pattern to have a desiredthickness by merely conducting a CMP process that stops spontaneously atthe organic spin-on-glass film. As such an organic spin-on-film has avery low dielectric constant, the problem of concentration of electricflux is avoided effectively and the signal delay associated with thestray capacitance of the multilayer interconnection structure issuccessfully eliminated.

Table 1 below shows the result of polishing experiments conducted by theinventor of the present invention with regard to the invention notedabove. In the experiments, various insulation films including an organicSOG (spin-on-glass) film, a plasma-CVD SiO₂ film and a plasma-CVD SiNfilm, are subjected to a CMP process, wherein the CMP process isconducted under various conditions optimized for polishing variousconductor layers including Cu, Al and W.

TABLE 1 [Cu] [Al] [W] plasma SiO₂ film 120 Å/min 130 Å/min 110 Å/minplasma SiN film 350 300 240 organic SOG film  10  12  13

Referring to Table 1, the CMP process was conducted under a condition[Cu] optimized for polishing a Cu layer, a condition [Al] optimized forpolishing an Al layer, and a condition [W] optimized for polishing a Wlayer, for each of a plasma SiO₂ film, a plasma SiN film and an organicSOG film, wherein an Al₂O₃ slurry was used in combination with an H₂O₂oxidant in the condition [Cu] and in the condition [Al], while an Al₂O₃slurry was used in combination with an oxidant of iron nitrate in thecondition [W]. In the condition [Cu], the platen was rotated at a speedof 60 rpm and the polishing was made under a pressure of 4.0 psi. In thecondition [Al], the platen was rotated at a speed of 50 rpm and thepolishing was made under a pressure of 5.0 psi. In the condition [W],the platen was rotated at a speed of 60 rpm and the polishing was madeunder a pressure of 5.0 psi.

As can be seen clearly in Table 1, the polishing rate of the organic SOGfilm is in the order of 10–13 Å/min throughout the conditions [Cu]-[W],while this polishing rate is remarkably smaller than the polishing ratefor polishing a plasma SiO₂ film or a plasma SiN film. In the case ofpolishing the organic SOG film, it was further confirmed that the filmis substantially free from scratches that are tend to be induced when aplasma-CVD SiO₂ film is polished.

The foregoing discovery indicates that the organic SOG film can be usedsuccessfully for a polishing stopper in a CMP process.

Another object of the present invention is to provide a method offabricating a semiconductor device, comprising the steps of:

forming an interlayer insulation film on a substrate;

forming a groove in said interlayer insulation film;

forming a conductor layer on said interlayer insulation film so as tofill said groove;

removing a part of said conductor layer covering said interlayerinsulation film by a chemical mechanical polishing process, to form aconductor pattern filling said groove; and

applying an insulation film of a liquid form on said interlayerinsulation film, such that said insulation film covers said conductorpattern.

Another object of the present invention is to provide a method offabricating a semiconductor device, comprising the steps of:

forming a first interlayer insulation film on a substrate;

forming a groove in said first interlayer insulation film;

forming a conductor layer on said first interlayer insulation film so asto fill said groove;

removing a part of said conductor layer covering said first interlayerinsulation film by a chemical mechanical polishing process, to form aconductor pattern filling said groove;

forming a second interlayer insulation film on said first interlayerinsulation film so as to cover said conductor pattern; and

planarizing said second interlayer insulation film by a chemicalmechanical polishing process.

Another object of the present invention is to provide a semiconductordevice, comprising:

a substrate;

a first interlayer insulation film formed on said substrate;

a first depression formed in said first interlayer insulation film;

a first conductor pattern filling said first depression;

a second interlayer insulation film formed on said first interlayerinsulation film so as to cover said first conductor pattern, said secondinterlayer insulation film having a planarized surface;

a second depression formed in said second interlayer insulation film;and

a second conductor pattern filling said second depression.

According to the present invention, the problem of short-circuitoccurring in the upper layer interconnection patterns is effectivelyeliminated even in such a case where there is a dishing in the lowerlayer interconnection pattern, by planarizing the interlayer insulationfilm that covers the lower layer interconnection pattern.

Other objects and further features of the present invention will becomeapparent from the following detailed description when read inconjunction with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A–1C are diagrams showing the process of forming a multilayerinterconnection structure having a damascene structure;

FIGS. 2A–2D are diagrams showing the problem caused in a conventionalmultilayer interconnection structure having a damascene structure;

FIGS. 3A–3N are diagrams showing the fabrication process of asemiconductor device according to a first embodiment of the presentinvention;

FIG. 4 is a diagram showing the effect of the multilayer interconnectionstructure of the first embodiment in comparison with a conventionalmultilayer interconnection structure;

FIGS. 5A–5N are diagrams showing the fabrication process of asemiconductor device according to a second embodiment of the presentinvention;

FIGS. 6A–6H are diagrams showing the fabrication process of asemiconductor device according to a third embodiment of the presentinvention; and

FIG. 7 is a diagram showing the effect of the second and thirdembodiments of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

FIGS. 3A–3N are diagrams showing the fabrication process of asemiconductor device according to a first embodiment of the presentinvention.

Referring to FIG. 3A, an SiO₂ film 22 is deposited on a Si substrate 21,on which an active device such as a MOSFET may be formed, by a plasmaCVD process with a thickness of about 300 nm, followed by a depositionof an SiN film 23 on the SiO₂ film 22 with a thickness of about 50 nm.

Next, in the step of FIG. 3B, an organic interlayer insulation film 24of an aromatic compound polymer such as the FLARE 2.0 (trade name) ofAllied Signal Corp. or a hydrocarbon polymer such as the SiLK of DowChemical, Inc., is deposited on the SiN film 23 by a spin-coatingprocess, typically with a thickness of about 400 nm. Further, an organicSOG film 25 is formed on the organic interlayer insulation film 24 by aspin-coating process typically with a thickness of about 50 nm.

In the step of FIG. 3B, the interlayer insulation film 24 and theorganic SOG film 25 are further subjected to a curing process togetherwith the underlying substrate 21 and the films 22 and 23, wherein thecuring process is conducted in an N₂ atmosphere at about 400° C. forabout 1 hour. The organic interlayer insulation film 24 thus formed hasa low dielectric constant of about 2.8, which is substantially lowerthan the dielectric constant of an SiO₂ film of about 4.1. Further, theorganic SOG film 25 thus formed also has a very low dielectric constantof about 3.0.

Next, in the step of FIG. 3C, a resist film 26A is formed on thestructure of FIG. 3B, followed by an exposure and developing process toform a number of resist openings 26B in the resist film 26A incorrespondence to the conductor pattern to be formed, and a plasmaetching process is applied in the step of FIG. 3D to the organic SOGfilm 25 and the organic interlayer insulation film 24 while using theresist film 24A as a mask. Thereby, it should be noted that the plasmaetching process for the organic SOG film 25 is conducted by using amixture of CF₄ and Ar for the etching gas, while the plasma etchingprocess for the organic interlayer insulation film 24 is conducted byusing O₂ for the etching gas.

In this foregoing patterning process, it should be noted that the resistfilm 26A is removed in the step of patterning the organic interlayerinsulation film 24 as a result of the plasma etching process that usesthe O₂ etching gas. Even in such a case, the patterning of the organicinterlayer insulation film 24 proceeds properly, as the organic SOG film25 patterned previously by the etching gas of CF₄ and Ar has aresistance against oxidation and works as an effective etching mask.

Next, in the step of FIG. 3E, a TiN film 26 is deposited on thestructure of FIG. 3D by a sputtering process typically with a thicknessof about 50 nm, and a Cu layer 27 is formed on the TiN film 26 by asputtering process with a thickness of about 800 nm.

Further, in the step of FIG. 3F, the structure of FIG. 3E is processedin a hydrogen atmosphere at about 400° C. for about 5 minutes to inducea reflowing in the Cu layer 27. As a reflowing, the Cu layer 27 fillsthe groove 24A completely.

Next, in the step of FIG. 3G, the part of the Cu layer 27 above theorganic SOG layer 25 is removed by a CMP process that uses a slurry ofAl₂O₃. More specifically, the CMP process of the Cu layer 27 isconducted by using H₂O₂ as an oxidant in combination with the foregoingAl₂O₃ slurry while setting the rotational speed of the platen of thepolishing apparatus to 60 rpm and the urging pressure to 4.0 psi. Byconducting the CMP process under such a condition, the organic SOG film25 remains substantially unetched as explained with reference to Table 1before, and the polishing stops spontaneously upon the exposure of theorganic SOG film 25. In other words, the organic SOG film 25 works as aneffective polishing stopper against the CMP process. In the process ofFIG. 3G, it should be noted that the conductor pattern 27A forms awiring pattern of a damascene structure in which the conductor pattern27A is embedded in the organic interlayer insulation film 24 and theorganic SOG film 25 thereon.

Next, in the step of FIG. 3H, an organic interlayer insulation film 28having a composition identical with the composition of the organicinterlayer insulation film 24 is provided on the structure of FIG. 3Gtypically with a thickness of about 100 nm by a spin-coating process,followed by a curing process conducted in an atmosphere of N₂ at about400° C. for about 1 hour. Further, an SiO₂ film 29 is deposited on theinterlayer insulation film 28 by a plasma CVD process with a thicknessof typically about 500 nm. The SiO₂ film 29 may be formed by an organicSOG film.

Next, in the step of FIG. 3I, a resist film 30 is formed on the SiO₂film 29, wherein the resist film 30 is subjected to exposure anddevelopment to form a window 30A.

Next, in the step of FIG. 3J, a contact hole 29A is formed in the SiO₂film 29 by a plasma etching process conducted while using the resistfilm 30 as a mask, such that the contact hole 29A penetrates through theSiO₂ film 29 and the organic interlayer insulation film 28 underneaththe SiO₂ film 29. In this step of FIG. 3J, a mixture of CF₄, CH₂F₂ andAr is used as an etching gas for the plasma etching process of the SiO₂film 29, while a mixture of O₂ and Ar is used as an etching gas for theplasma etching process of the organic interlayer insulation film 28.When etching the organic interlayer insulation film 28, the resist film30 is removed by the etching gas containing O₂. Even in such a case, theetching of the organic interlayer insulation film 28 to form the contacthole 29A therein proceeds properly, as the SiO₂ film 29 thereon acts asan effective etching mask.

Next, in the step of FIG. 3K, a TiN film 31 is formed on the structureof FIG. 3J by a sputtering process with a thickness of about 50 nm, suchthat the TiN film 31 covers the side wall of the contact hole 29A.Further, a Cu layer 32 is formed on the TiN film 31 by a sputteringprocess with a thickness of typically about 1000 nm.

Next, in the step of FIG. 3L, the structure of FIG. 3K is annealed in anatmosphere of H₂ at about 400° C. for about 5 minutes, to cause areflowing in the Cu layer 32, such that the Cu layer 32 fills thecontact hole 29A completely. Further, in the step of FIG. 3M, the partof the Cu layer 32 locating above the SiO₂ film 29 is removed by a CMPprocess, to form a conductive plug 32A filling the contact hole 29A.Further, by repeating the steps of FIGS. 3A–3G on the structure of FIG.3M, a damascene structure shown in FIG. 3N is obtained in which it willbe noted that a number of conductor patterns 33A embedded in an organicinterlayer insulation film 33 covered by an organic SOG film 34.

FIG. 4 shows the stray capacitance of the conductor pattern in themultilayer interconnection structure of FIG. 3N for various separationintervals of the conductor patterns, in comparison with a case in whichan ordinary plasma-CVD SiO₂ film is used in place of the organic SOGfilm 25 or 34, wherein the open circles represent the result for thecase of using the organic SOG film while the solid circles represent theresult for the case of using the plasma-CVD SiO₂ film. In both cases, itis assumed that the interconnection patterns have a width of 0.4 μm.

Referring to FIG. 4, it can be seen that the stray capacitance of thestructure of FIG. 3N represented by the open circles is smaller than thestray capacitance of the conventional case represented by the solidcircles and that the difference is pronounced with decreasing separationof the interconnection patterns.

Second Embodiment

As explained with reference to FIGS. 2A–2D, there is a tendency, in amultilayer interconnection structure formed by a damascene process, thata wide conductor pattern undergoes a dishing. When such a dishing iscaused, there may be a short circuit in the upper conductor patternsformed above the wide conductor pattern as explained before. Thereby,the yield of semiconductor fabrication is inevitably decreased.

Hereinafter, a fabrication process of a semiconductor device accordingto a second embodiment of the present invention for eliminating theforegoing problem will be described with reference to FIGS. 5A–5M.

Referring to FIG. 5A, an SiO₂ film 42 is deposited on a Si substrate 41,on which an active device such as a MOSFET may be formed, by a plasmaCVD process with a thickness of about 200 nm, and an organic interlayerinsulation film 43 is deposited on the SiO₂ film 42 by a spin-coatingprocess typically with a thickness of about 400 nm. The organicinterlayer insulation film 43 may be any of an aromatic polymer such asthe FLARE 2.0 (trade name) of Allied Signal Corp. noted before or ahydrocarbon polymer such as SILK (trade name) of Dow Chemical, Inc. Asnoted previously, the organic interlayer insulation film 43 thus formedhas a very low dielectric constant of about 2.8 and is suitable for theinterlayer insulation film of a high-speed semiconductor device.

In the structure of FIG. 5A, it should be noted that a polishing stopperfilm 44 of an organic SOG is formed on the organic interlayer insulationfilm 43 by a spin-coating process with a thickness of typically about 50nm. Alternately, it is possible to form the foregoing polishing stopperfilm 44 by a plasma-CVD SiO₂ film having a thickness of about 100 nm.

Next, in the step of FIG. 5B, a resist pattern 45A having an opening 45Bis formed on the structure of FIG. 5A, and a plasma etching process isconducted in the step of FIG. 5C while using the resist film 45A as amask, to form an opening 44A in the polishing stopper film 44 incorrespondence to the foregoing resist opening 45A. It should be notedthat the plasma etching process of the polishing stopper film 44 isconducted by using a mixture of CF₄, CH₂F₂ and Ar as an etching gas.

Next, in the step of FIG. 5D, the etching gas is switched to a mixtureof O₂ and Ar, and the plasma etching process is continued to form anopening 43A in the organic interlayer insulation film 43 incorrespondence to the opening 44A while using the polishing stopper film44 as a mask. It should be noted that the opening 43A thus formedexposes the underlying SiO₂ film 42. As a result of the plasma etchingprocess of the organic interlayer insulation film 43 by the etching gasthat contains O₂, the resist film 45 is removed simultaneously.

Next, in the step of FIG. 5E, a film 45 of a refractory metal compoundsuch as TiN is deposited on the structure of FIG. 5D by a sputteringprocess with a thickness of about 50 nm, followed by a furthersputtering deposition process of a Cu layer 46 on the TiN film 45 with athickness of about 800 nm.

Next, in the step of FIG. 5F, the structure of FIG. 5E is subjected to athermal annealing process conducted in an atmosphere of H₂ at about 400°C. for about 5 minutes under a reduced pressure of about 0.1 Torr, tocause a reflowing in the Cu layer 46. Further, in the step of FIG. 5G, aCMP process is applied to the Cu layer 46 while using Al₂O₃ as a slurryand the part of the Cu layer 46 above the polishing stopper film 44 isremoved. As explained previously with reference to Table 1, thepolishing stopper film 44 of the organic SOG shows an excellentresistance against the polishing, and the CMP process stopsspontaneously upon the exposure of the organic SOG film 44 as indicatedin FIG. 5G. Of course, it is possible to stop the CMP process with highprecision in the state of FIG. 5G upon the exposure of the film 44 whenan ordinary plasma-CVD film is used for the polishing stopper film 44.As a result of the CMP process, a Cu pattern 46A filling the opening 43Ais obtained as a damascene structure. As explained with reference toFIG. 2B, such a Cu pattern 46A shows a dishing in a surface 46B thereofwhen the Cu pattern 46A is formed to have an increased width.

Next, in the step of FIG. 5H, another organic interlayer insulation film47 is formed on the structure of FIG. 5G by a spin-coating process witha thickness of about 200 nm. Further, an SiO₂ interlayer insulation film48 is formed on the organic interlayer insulation film 47 by aplasma-CVD process with a thickness of about 500 nm. It should be notedthat the foregoing organic interlayer insulation film 47 may be formedof an aromatic polymer or a hydrocarbon polymer used for forming theorganic interlayer insulation film 43. As the interlayer insulation film47 is formed by a spin-coating process, the surface of the interlayerinsulation film 47 is flat even when there is a dishing in theunderlying interconnection pattern 46A. Associated with this, theinterlayer insulation film 48 on the interlayer insulation film 47 has aplanarized surface.

Next, in the step of FIG. 5J, a contact hole 48A is formed through theinterlayer insulation film 48 and further through the interlayerinsulation film 47 so as to expose the surface 46B of the conductorpattern 46A. Further, a refractory film 49 of a refractory metalcompound such as TiN is formed on the structure of FIG. 5J in the stepof FIG. 5K typically with a thickness of about 50 nm, After theformation of the TiN film 49, a sputtering process of a Cu layer 50 isconducted also in the step of FIG. 5K with a thickness of about 800 nm.It should be noted that the foregoing step of forming the contact hole48A is conducted first by applying a plasma etching process to the SiO₂film 48 while using a mixture of CF₄, CH₂F₂ and Ar as an etching gas,followed by applying a plasma etching process to the underlying organicinterlayer insulation film 47 while using a mixture of O₂ and Ar as anetching gas.

The Cu layer 50 thus formed is then subjected to a thermal annealingprocess conducted in the step of FIG. 5L at about 400° C. in theatmosphere of H₂ under a pressure of about 0.1 Torr for about 5 minutes,wherein the Cu layer 50 thus treated causes a reflowing and fills thecontact hole 48A completely.

Next, in the step of FIG. 5M, the part of the Cu layer 50 above the SiO₂interlayer insulation film 48 is removed by a CMP process, to form a Cuplug 50A filling the contact hole 48A.

Further, in the step of FIG. 5M, the steps of FIGS. 3A–3G are repeatedto form a multilayer interconnection structure represented in FIG. 5N,wherein the multilayer interconnection structure of FIG. 5N includes anumber of conductor patterns 54A embedded in an organic interlayerinsulation film 51 by a damascene process. In the example of FIG. 5N, itshould be noted that the organic interlayer insulation film 51 carries apolishing stopper film 52 of an organic SOG film or a plasma-CVD SiO₂film. In making the structure of FIG. 5N, it is also possible to carryout the steps of FIGS. 5A–5G on the structure of FIG. 5M. In thestructure of FIG. 5N, the conductor pattern 54A makes an electricalcontact with the underlying conductor pattern 46A via the conductiveplug 50A.

In the present embodiment, the conductor pattern 54A is formed on theinterlayer insulation film 48 having a planarized surface. Thus, evenwhen there exists a significant dishing in the surface 46B of theunderlying conductor pattern 45A, there is no substantial risk that theconductor patterns 54A cause a short-circuit.

In the present embodiment, it should be noted that the conductor pattern54A may extend in the same direction as the underlying conductor pattern46A or in a different direction. For example, the conductor pattern 54Amay extend perpendicularly to the underlying conductor pattern 46A.Further, it will be noted that the conductor patterns 54A are repeatedin the interlayer insulation film 51 with a pitch smaller than a pitchof repetition of the conductor patterns 46A.

Third Embodiment

FIGS. 6A–6H show a fabrication process of a semiconductor deviceaccording to a third embodiment of the present invention.

Referring to FIG. 6A, the step of FIG. 6A corresponds to the step ofFIG. 5G and an organic interlayer insulation film 63 is formed on a Sisubstrate 61, on which an active device such as a MOSFET is formed, viaan intervening SiO₂ film 62.

On the organic interlayer insulation film 63, a polishing stopper film64 of an organic SOG film or a plasma-CVD SiO₂ film is provided, and arefractory conductor film 65 of a refractory metal compound such as TiNis provided so as to cover a side wall and a bottom surface of a grooveformed in the polishing stopper film 64 and the organic interlayerinsulation film 63. Thereby, the groove is filled by a Cu pattern 66Aformed in contact with the refractory conductor film 65 by a damasceneprocess including a deposition of a Cu layer and a CMP process thereof,similarly as before. As a result of the chemical mechanical polishingprocess, a dishing is formed on a surface 66B of the Cu pattern 66A.

Next, in the step of FIG. 6B, an SiN film 67 is deposited on thestructure of FIG. 6A by a plasma-CVD process with a thickness of about50 nm, and an interlayer insulation film 68 of SiO₂ is deposited on theSiN film 67 by a plasma-CVD process with a thickness of about 1000 nm.In the step of FIG. 6B, it should be noted that the SiN film 67 works asa diffusion barrier preventing a diffusion of Cu from the Cu pattern 66Ato the SiO₂ film 68.

Next, in the step of FIG. 6C, the SiO₂ interlayer insulation film 68 ofFIG. 6B is planarized by a CMP process that uses a slurry of SiO₂.Further, in the step of FIG. 6D, a plasma etching process using amixture of CF₄, CH₂F₂ and Ar, is applied to the interlayer insulationfilm 68 to form a contact hole 68A penetrating through the interlayerinsulation film 68 and the underlying SiN film 67 such that the contacthole 68A exposes the surface 66B of the conductor pattern 66A.

Next, in the step of FIG. 6E, a refractory conductor film 69 of arefractory metal compound such as TiN is deposited on the structure ofFIG. 6D by a sputtering process with a thickness of about 50 nm,followed by a sputter deposition of a Cu layer 70 with a thickness ofabout 800 nm.

Next, in the step of FIG. 6F, the structure of FIG. 6E is subjected tothermal annealing process conducted in the atmosphere of H₂ at about400° C. for about 5 minutes under a pressure of about 0.1 Torr, to causea reflowing in the Cu layer 68, followed by a CMP process conducted byusing a slurry of Al₂O₃ to remove the part of the Cu layer 68 locatingabove the SiO₂ interlayer insulation film 68, to form a Cu plug 70Afilling the contact hole 68A. It should be noted that the CMP process ofthe Cu layer 70 stops spontaneously upon the exposure of the SiO₂interlayer insulation film 68. As a result of the CMP process, the SiO₂,interlayer insulation film 68 has a planarized surface irrespective ofthe dishing in the underlying conductor pattern 66A.

Next, in the step of FIG. 6H, the steps of FIGS. 3A–3G describedpreviously are conducted on the structure of FIG. 6G, and a multilayerinterconnection structure including a number of conductor patterns 73Aembedded in an organic interlayer insulation film 71 by a damasceneprocess, is obtained. In the example of FIG. 6H, it will be noted thatthe organic interlayer insulation film 71 carries thereon a polishingstopper film 72 of an organic SOG film or a plasma-CVD SiO₂ film.

In the present embodiment, too, the problem of short-circuit of theconductor patterns 73A is effectively avoided by planarizing theinterlayer insulation film 68.

FIG. 7 shows the fabrication yield of the semiconductor device accordingto the second and third embodiments of the present invention incomparison with the yield for a case in which the same semiconductordevice is formed by the conventional process of FIGS. 2A–2D.

Referring to FIG. 7, the conventional yield of 40–50% is increased toalmost 100% by employing the present invention. Further, the tendency ofdecrease of the yield with decreasing width of the conductor patterns iseliminated by employing the present invention.

In the present embodiment, too, the conductor pattern 73A may extendparallel with the underlying conductor pattern 66A or in a directionobliquely to the conductor pattern 66A. For example, the conductorpattern 73A may extend perpendicularly to the conductor pattern 66A.Further, it will be noted that the conductor patterns 73A are repeatedin the interlayer insulation film 71 with a pitch smaller than a pitchof repetition of the conductor patterns 65A.

In the embodiments described heretofore, it should be noted that theconductor layer 27 and 32 or 46 and 50 may be formed also by anelectroplating process, an electroless plating process, or a CVDprocess. Further, the conductor layer may be formed also of Al or an Alalloy.

Further, the present invention is not limited to the embodimentsdescribed heretofore, but various variations and modifications may bemade without departing from the scope of the invention.

The present application is based on Japanese priority application No.10-75938 filed on Mar. 24, 1998, the entire contents of which are herebyincorporated by reference.

1. A semiconductor device comprising: a substrate; an interlayerinsulation film formed on said substrate; another insulation film beingformed of an organic spin-on-glass formed on said interlayer insulationfilm; a uniform depression penetrating through said another insulationfilm and reaching said interlayer insulation film; and a conductorpattern filling said depression; said conductor pattern having a topsurface continuous with a top surface of said another insulation film.2. A semiconductor device as claimed in claim 1, wherein said conductorpattern is formed of Cu.
 3. A semiconductor device as claimed in claim1, wherein said interlayer insulation film is formed of a hydrocarbonpolymer compound.
 4. A semiconductor device as claimed in claim 1,wherein said interlayer insulation film is formed of an aromatic polymercompound.
 5. A semiconductor device as claimed in claim 1, furthercomprising a conductor film between said depression and said conductorpattern, said conductor film covering said depression in conformity witha shape of said depression.
 6. A semiconductor device as claimed inclaim 1, wherein said depression penetrates through said interlayerinsulation film.
 7. A semiconductor device, comprising: a substrate; afirst interlayer insulation film formed on said substrate; a firstdepression formed in said first interlayer insulation film; a firstconductor pattern filling said first depression, said first conductorpattern having a dishing surface; a second interlayer insulation filmbeing formed of an organic spin-on-glass formed on said first interlayerinsulation film so as to cover the dishing surface of said firstconductor pattern, said second interlayer insulation film having aplanarized surface; a second depression formed in said second interlayerinsulation film; and a second conductor pattern filling said seconddepression.
 8. A semiconductor device, comprising: a substrate; a firstinterlayer insulation film formed on said substrate; a first depressionformed in said first interlayer insulation film; a first conductorpattern filling said first depression, said first conductor patternhaving a dishing surface; a second interlayer insulation film formed onsaid first interlayer insulation film so as to cover the dishing surfaceof said first conductor pattern, said second interlayer insulation filmhaving a planarized surface; a second depression formed in said secondinterlayer insulation film; and a second conductor pattern filling saidsecond depression, wherein said second interlayer insulation filmincludes a first film of an organic insulation film having a planarizedtop surface, and a second film formed on said first film.
 9. Asemiconductor device, comprising: a substrate; a first interlayerinsulation film formed on said substrate; a first depression formed insaid first interlayer insulation film; a first conductor pattern fillingsaid first depression, said first conductor pattern having a dishingsurface; a second interlayer insulation film formed on said firstinterlayer insulation film so as to cover the dishing surface of saidfirst conductor pattern, said second interlayer insulation film having aplanarized surface; a second depression formed in said second interlayerinsulation film; and a second conductor pattern filling said seconddepression, wherein said first conductor pattern is repeated in saidfirst interlayer insulation film with a first pitch, and said conductorpattern is repeated in said second interlayer insulation film with asecond pitch smaller than said first pitch.
 10. A semiconductor devicecomprising: a substrate; a first interlayer insulation film formed onsaid substrate; a first depression formed in said first interlayerinsulation film; a first conductor pattern filling said firstdepression; a second interlayer insulation film formed on said firstinterlayer insulation film so as to cover said first conductor pattern,said second interlayer insulation film having a planarized surface; asecond depression formed in said second interlayer insulation film; anda second conductor pattern filling said second depression, wherein saidfirst conductor pattern extends in said first interlayer insulation filmin a first direction and wherein said second pattern extends in saidsecond interlayer insulation film in a second direction different fromsaid first direction.
 11. A semiconductor device comprising: asubstrate; a first interlayer insulation film formed on said substrate;a first depression formed in said first interlayer insulation film; afirst conductor pattern filling said first depression; a secondinterlayer insulation film formed on said first interlayer insulationfilm so as to cover said first conductor pattern, said second interlayerinsulation film having a planarized surface; a second depression formedin said second interlayer insulation film; and a second conductorpattern filling said second depression, wherein said first conductorpattern extends in said first interlayer insulation film in a firstdirection and wherein said second conductor pattern extends in saidsecond interlayer insulation film in said first direction.
 12. Asemiconductor device, comprising: a substrate; a first interlayerinsulation film formed on said substrate; a first depression formed insaid first interlayer insulation film; a first conductor pattern fillingsaid first depression, said first conductor pattern having a dishingsurface; a second interlayer insulation film formed on said firstinterlayer insulation film so as to cover the dishing surface of saidfirst conductor pattern, said second interlayer insulation film having aplanarized surface; a second depression formed in said second interlayerinsulation film; and a second conductor pattern filling said seconddepression, wherein said second interlayer insulation film is aninorganic insulation film having a planarized top surface.
 13. Asemiconductor device as claimed in claim 12, wherein said secondinterlayer insulation film comprises a first film conformal to a shapeof said first conductor pattern, and a second film formed on said firstfilm, said second film having a planarized top surface.
 14. Asemiconductor device as claimed in claim 13, wherein said first filmcomprises an SiN film and said second film comprises an SiO₂ film.